Blast overbreak measurement by light sectioning

Summary In this new method for measuring the cross-section of tunnels and other excavations, the opening is outlined by a plane of light projected from a conical mirror. The image is recorded on videotape, enhanced, then measured by microcomputer. The measured profile is compared automatically with the specified profile to give values for overbreak and underbreak.Trials in Mexican tunnels and at an underground mine in Canada have evaluated the technique in relation to traditional mechanical, photographic, and surveying alternatives. Results indicate that the light sectioning method requires less than a minute per profile and no surveying skills. Costs are low, and the measurements are accurate to within a centimetre or two. Using the same photoanalysis technique and software, rock quality can be measured at the same time and place as overbreak, which helps the engineer to decide whether overbreak is caused by geological conditions or by deficiencies in blasting.     

The RbSr isotope system as an index of origin and diagenetic evolution of southern Pacific red clays

Morphological, mineralogical, chemical and RbSr isotopic studies have been made on Fesmectites (nontronites) from southern Pacific red clays cored near the Marquisas Islands. These minerals have at the top of the core, an ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of 0.70917 ± 0.00007, which indicates an authigenic origin in isotopic equilibrium with seawater. Weak leaching experiments with 1N HCl show that the nontronites also contain a volcanic component with a lower ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio which, combined with the morphology of the particles, suggests a transportation by bottom currents of clay formed elsewhere.During burial, the nontronites experience diagenetic modifications resulting in an increase in Fe, K and Rb contents, a concomitant decrease of Mg, Ca, Ti, Na and Sr, and a preferential migration of radiogenic ⁸⁷Sr from the clays into the surrounding pore waters.The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of the Sr adsorbed on the outermost surfaces of the nontronites does not change with depth in the core, and is, therefore, independent of diagenetic influence, which is rather characterized by the ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of the interstitial waters. The isotopic composition of both the adsorbed Sr and that of the pore fluids may yield useful information on the crystallization environment and subsequent history of deep sea red clays.     

Datation isotopique des cristallisations successives d' un socle cristallin et cristallophyllien (Haute Moulouya,Moyen Maroc)

Résumé L'étude pétrographique et microtectonique a permis d'établir la chronologie relative des épisodes tectono-métamorphiques et intrusifs qui affectent le socle cristallin et cristallophyllien de la Haute Moulouya dans le Moyen Maroc. Ces différents épisodes ont pu être datés par la méthode rubidium-strontium.Ainsi, deux phases tectono-métamorphiques ont pu être distinguées dans le socle cristallophyllien et attribuées au Dévonien supérieur, la première se terminant vers 366±7 M. a. (avec ⁸⁷Rb=1,42 × 10^–11 an^–1). Les épisodes intrusifs se situent dans le Viséen et le Namurien; ils débutent par la mise en place de granodiorites vers 347±17 M. a. et se poursuivent par celle de granites alcalins vers 329±6 M. a. et de granites calco-alcalins vers 319±6 M. a. L'ensemble de ces formations est ensuite affecté par des cisaillements contemporains de cristallisations pneumatolytiques; les néocristallisations liées à cette dernière phase de déformation ont pu être datées de 315 M. a. dans certains granites. Des venues filoniennes de pegmatite vers 310 M. a., de granite à structure graphique et d'aplite à 302±3 M. a. sont liées a ce phénomène tardif.La confrontation des analyses isotopiques et microtectoniques permet d'apprécier l'importance de certains épisodes tectono-métamorphiques sur l'homogénéisation isotopique du strontium contenu dans les roches totales, les minéraux ou les fractions fines < 2 .

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A petrographic and microstructural study of the crystalline and metamorphic basement rocks of the Haute Moulouya region in the central part of Morocco revealed a chronology of tectono-metamorphic and intrusive events. These events have been dated by the Rb-Sr method.The crystalline basement is affected by two tectono-metamorphic episodes; the first occurred during the Upper Devonian at 366±7 m. y. (with ⁸⁷Rb=1.42 × 10^–11 y^–1). These events are followed by intrusions which are Visean and Namurian in age, granodiorites crystallized at 347±17 m. y. and are followed by alkaline granites at 329±6 m. y. and by calco-alkaline granites at 319±6 m. y. A pneumatolysis then accompanied shearing of the rocks. The degradation of preexisting minerals and the formation of new minerals, especially muscovites, in some granites occurred around 315 m. y. This event is also related to intrusions of pegmatites at 310 m. y. and granites with graphic structures and aplites at 302±3 m. y.The comparison of the isotopic and microstructural results also allowed estimation of the influence of the different tectono-metamorphic episodes on the strontium isotopic homogeneity of whole rocks, minerals and fine fractions <2 .

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Zusammenfassung Eine petrographische Gefügeanalyse der kristallinen und metamorphen Basisgesteine der Haute Moulouya Region in Zentralmarokko ergab eine Chronologie der tektono-metamorphen und intrusiven Vorgänge. Diese Ereignisse wurden mit Hilfe der Rb-Sr-Methode datiert.Die kristalline Basis ist von zwei tektono-metamorphen Phasen beeinflußt. Die erste dieser Phasen entstand während des Oberdevons vor 366±7 mJ (mit ⁸⁷Rb = 1.42 × 10^–11 mJ). Beiden Phasen folgten Intrusionen mit Altern von Visé und Namur. Dabei entstanden Granodiorite in einem Alter von 347±17 mJ. Diesen folgten Alkaligranite mit 329 ±6 mJ und schließlich Kalkalkaligranite mit 319±6 mJ; darauf setzte ein Scherbeanspruchung ein, die von einer Pneumatolyse begleitet wurde. Der Zerfall der älteren Mineralphasen sowie die Bildung von neuen Mineralen (besonders Muscovit) in manchen Graniten entstand vor etwa 315 Millionen Jahren. Dieser Vorgang ist auch mit der Intrusion von Pegmatiten vor etwa 310 mJ in Beziehung zu setzen. Spätere Intrusionen von Graniten mit schriftgranatischem Gefüge und Apliten erfolgte etwa vor 302±3 mJ.Der Vergleich von Isotopenverteilung und mikrostrukturellem Gefüge lieferte eine Basis für die Einschätzung der Beeinflussung durch die verschiedenen tektono-metamorphen Phasen auf die Homogenität der Strontiumisotope im gesamten Gestein, in den Mineralien und in den feinen Fraktionen <2 .

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Haute ulu, kk, - . - . - . (3667 ⁸⁷Rb= 1,42 &#x0445; 10^–11–1). . 34717 ; 3296 , 3106 . — — 350 . , 310 . 3023 . - , , 2.

     

Utilisation de la méthode rubidium-strontium pour la datation de niveaux sédimentaires du Précambrien supérieur de l'Adrar mauritanien (Sahara occidental) et la mise en évidence de transformations précoces des minéraux argileux

Amineralogical-geochronological study has been made of sedimentary levels I₂ and I₅ in the upper Precambrian of the Adrar, Mauritania, showing that clay minerals can be used for geochronology. This is, however, only possible where early diagenesis has homogenised the ⁸⁷Sr/⁸⁶Sr ratio of clay minerals and interstitial waters. Rocks whose clay minerals consist of unaltered mica or illite are not suitable for this approach, as is the case for sediments rich in detrital feldspars: carbonates may however be used.Ages of 964 ± 32 M.Y. (I₂) and860± 35 M.Y. (I₅) were obtained using a⁸⁷Rb decay constant of 1.47 × 10?11 yr^?1, confirming that the beginning of the late Precambrian sedimentation in the Adrar may be placed at 1000 M .Y.     

High-resolution magnetostratigraphy of four sediment cores from the Greenland Sea–I. Identification of the Mono Lake excursion, Laschamp and Biwa I/Jamaica geomagnetic polarity events

High-resolution magnetostratigraphic analysis of three sediment cores from the base of the volcanic seamount Vesteris Banken in the Greenland Basin and one core from the Jan Mayen Fracture Zone revealed records of three pronounced geomagnetic events within the last 200 ka. Dating by stable carbon and oxygen isotope analysis, AMS¹⁴C measurements and biostratigraphic data (foraminifera abundances) yielded ages of 28–27 ka for the Mono Lake excursion, 37–33 ka for the Laschamp event, and 189–179 ka for the Biwa I event. In at least one of the cores the Laschamp event exhibits a full reversal of the local geomagnetic field vector. The same is true of the Biwa I event, documented in one of the cores.     

Wave climatology and extreme value analysis for the Baltic Sea area off the Warnemünde harbour entrance

Ocean Dynamics - A numerical wave model was used to determine the wave climate in the southern Baltic Sea. The basic data derived from wave hindcasts were evaluated statistically. Climate graphs...     

Time dependent deformations during tunnelling and stability of tunnel faces in fine-grained soils under groundwater

The measures required for driving a tunnel below the groundwater table depend on the permeability of the soil. In coarse-grained, highly permeable soils additional measures, for example compressed-air support combined with a reduction of the permeability of the soil, e.g. induced by grouting, are necessary. Compared to this, it is possible to do without such measures in fine-grained, cohesive soils because of the increased short-term stability of the tunnel face under undrained conditions. In this publication the results of 3-dimensional finite-element calculations are presented to show the influence of the permeability of the soil and also the rate of the tunnel driving on the deformations around the tunnel as well as on the ground surface. The calculated deformations can furthermore be considered as an indicator for the time dependent stability of the tunnel face due to a higher redistribution of stresses and by that an enlargement of the plasticized zone. Usually the stability of the tunnel face is reduced by the presence of water because of the flow of water towards the tunnel. In low permeable soils undrained conditions prevail immediately after an excavation step. In this case relatively high stability-ratios may occur. The stability of the tunnel face will be reduced with increasing time until reaching the lower boundary of possible values, possibly leading to failure. If calculations are done under the assumption of drained conditions, the real stability of the tunnel face during construction may substantially exceed that of the calculated one. On the other hand, if calculations are done for undrained conditions, the effective stability may lie on the unsafe side [10]. There is therefore a big demand to optimize the method of investigating deformations around the tunnel, so as to ensure a safe tunnel excavation on the one hand and to guarantee a cost-effective process on the other. In this paper the tunnelling process is modelled by a step-by-step excavation under atmospheric conditions. The soil is described by a material model which distinguishes between primary and unload-reload stress paths and also accounts for stress-dependent stiffness parameters. The failure criterion is described by the Mohr-Coulomb criterion that considers cohesion, friction angle and angle of dilatancy.     

Influence of the initial water content and dry density on the soil–water retention curve and the shrinkage behavior of a compacted clay

The paper presents the results of an experimental study on the effects of the initial water content and dry density on the soil–water retention curve and the shrinkage behavior of a compacted Lias-clay. The initial conditions after compaction (initial water content and initial dry density) have been chosen on the basis of three Proctor tests of different compaction efforts. According to the eight chosen initial conditions clay samples have been compacted statically. The relation between total suction and water content was determined for the drying path starting from the initial conditions without previous saturation of the specimens. A chilled-mirror dew-point hygrometer was used for the suction measurements. For the investigation of the shrinkage behavior cylindrical specimens were dried to desired water contents step-by-step without previous saturation. The volume of the specimens was measured by means of a caliper. Based on the test results the influence of different initial conditions on the soil suction and the shrinkage behavior is analyzed. The soil–water retention curves obtained in terms of the gravimetric water content are independent of the initial dry density. At water contents above approximately 11–12.5% a strong influence of the compaction water content is observed. At smaller water contents, the soil–water retention curve is independent of the compaction water content. The results of the shrinkage tests show that the influence of the compaction dry density on the shrinkage behavior is negligible. Similar to the drying behavior of saturated samples a primary and a residual drying process could be distinguished. The primary drying process is strongly influenced by the initial water content. In contrast, the rate of the volume change of the residual drying process is unaffected by the initial water content.     

A method for estimating vegetation change over time and space

Plant diversity is used as an indicator of the well-being of vegetation and ecological systems. Human activities and global change drive vegetation change in composition and competition of species through plant invasions and replacement of existing species on a given scale. However, species diversity indices do not consider the effects of invasions on the diversity value and on the functions of ecosystems. On the other hand, the existing methods for diversity index can not be used directly for cross-scale evaluation of vegetation data. Therefore, we proposed a 3-dimensional model derived from the logistic equation for estimating vegetation change, using native and non-native plant diversity. The two variables, based on the current and the theoretical maximum diversity of native plants on a given scale, and the result of the model are relative values without units, and are therefore scale-independent. Hence, this method developed can be used directly for cross-scale evaluations of vegetation data, and indirectly for estimating ecosystem or environmental change.